"Well, I don't remember all of them exactly. I think there's a list in the trainer guide in your backpack. But, for instance... water and grass both erode rock, but rock resists fire. Flying is immune to ground. Bugs eat grass. Psychic is strong against fighting...

"Oh, yeah, and normal type and ghost type are immune to each other. That's a bit of a weird one, but it's important to remember."